Abstract
The aim of the study was to analyze the diet and feeding strategies of 0+ perch, Perca fluviatilis L., in two lakes (Gosławskie and Dołgie Wielkie) with different trophic and thermal regimes. Water temperature was higher in Lake Gosławskie (Mann-Whitney test, P<0.01), but oxygen concentration was similar in both lakes (Mann-Whitney U test, P<0.05). The mean abundance, biomass, and species richness of zooplankton during the study period were statistically significantly lower in Lake Gosławskie (test U Mann-Whitney, P < 0.0001. The share of perch with empty digestive tracts was very low. The fish from Lake Dołgie Wielkie had higher condition factors (mean 1.87) than did those from Lake Gosławskie (1.73). The analysis of the size structure of the prey consumed by perch from the two lakes indicated that the fish employed different foraging strategies. In Lake Dołgie Wielkie the perch consumed a large quantity of small plankton organisms (copepodites and Daphnidae) that occurred in large quantities, while in Lake Gosławskie, where zooplankton abundance was low, the basic diet comprised larger organisms (Sida crystallina, larval Chironomidae). Perch feeding intensity in Lake Dołgie Wielkie was positively correlated with body length, while in Lake Gosławskie it remained at the same level.